275 RE-MATING IN MIGRATORY WIGEON ANAS PENELOPE CARL MITCHELL Mitchell C. 1997. Re-mating in migratory Wigeon Anas penelope. Ardea 85: 275-277. This note describes re-mating in migratory Wigeon Anas penelope in sub­ sequent winters. Three pairs, out of five cases where both male and female partners returned to the study area, reformed in the following winter. Key words: Anas penelope - pair bond - re-mating - divorce The Wildfowl & Wetlands Trust, Slimbridge, Glos., GL2 7BT, U.K.; E­ mail [email protected] Seasonal pair bonds are characteristic of migra­ adults. A number of behavioural cues were used tory Holarctic ducks (Anas, Aythya, Mergus, Aix), to determine the existence of pairs, especially with pair bonds established during the winter pe­ courtship behaviour, maintenance of proximity, riod or the spring migration after the resurgence but also including synchronized vigilance and of sexual behaviour (Weller 1965) and adoption of feeding behaviour. a nuptial plumage. Typically, cJ cJ desert their Wigeon wintering on the refuge depart in mates during the breeding season (McKinney spring for Icelandic, northern Scandinavian and 1986) and leave the breeding areas to moult (often Russian breeding grounds (Owen & Mitchell hundreds of kilometres away), leaving the Q Q to 1988) returning from September. Daily checks for care for the ducklings alone. New pair bonds form colour-ringed Wigeon were made during winters while the birds are in flocks on the wintering 1988/89-1991/92 from September to April with quarters. Females are strongly philopatric, and particular emphasis on establishing liaisons be­ each cJ follows his mate back to her familiar nest­ tween marked individuals. It is highly likely that ing area (see Rohwer & Anderson 1988 for a re­ if a marked Wigeon was present at the study site it view). Whether or not the cJ and Q should re­ would have been seen. The date of pair formation mate the next year if both survive is an interesting with a particular partner was taken as the first of question, which has been recently reviewed by multiple sightings of when the pair were seen to­ Ens et at. (1996). According to Williams & gether exhibiting the behavioural cues outlined McKinney (1996) there are few published studies above. on this question regarding Anas that reunite on A total of twelve pairs of individually marked the wintering grounds. This study investigated re­ Wigeon were identified. Three pairs, out of five mating in individually-marked migratory Wigeon, cases where both male and female partners re­ wintering in south Scotland. turned to the study area, reformed in the follow­ Eastpark Farm (Dumfries and Galloway, ing winter. On two out of three occasions when 54°58'N, 3°26'W) supports c. 500 Wigeon, and pair bonds were re-established, the QQ were seen many feed and roost in a field of c. 7 ha (the study first and the cJ cJ were recorded subsequently. site) offering close observation facilities. During Pair reformation occurred within one, seven and 1988-1991, 87 Wigeon were caught using a baited 23 days of both partners first being observed. trap and were marked with a metal ring and an in­ Nine pairs of Wigeon (that had formed pair dividually recognizable coloured, plastic leg bonds) did not re-form their bonds in following band. Observations in the months following ring­ winters. In four cases, one of the partners was not ing revealed persistent pair bonds between certain recorded amongst the returning flock. In three ca- 276 ARDEA 85(2), 1997 ses, neither partner was recorded at Eastpark The cJ cJ may potentially make an informed Farm in subsequent winters. It is not known if the choice about re-mating, and, in order to maximize pairs reformed at another wintering site, however, reproductive output, it would be advantageous to it is perhaps even more likely that some marked know if his mate has reared young successfully. individuals were shot between winter periods. In Conspicuous male ducks do not usually associate two cases, Wigeon which had formed a pair bond with 9 9 after the onset of incubation (presum­ (in one winter) were seen in the flock in the fol­ ably to reduce predation risk), however, observa­ lowing winter but were not paired. Individuals tions of individually-marked breeding Wigeon in from both pairs eventually formed bonds with Scotland showed that male Wigeon sometimes other Wigeon present in the flock. accompanied their mates and broods in the first There are few records of known pairs of mi­ few days after hatching. Soon afterwards, the gratory Anas species re-forming bonds with ma­ cJ cJ left the breeding area (R. Duncan in iitt.). tes from previous years, and this may be partly at­ Thus, some cJ cJ may gain prior knowledge of the tributable to lack of investigation (Williams & reproductive success of their mate before depart­ McKinney 1996). The relatively high degree of ing to moult. winter site fidelity shown by some dabbling ducks Evidence from this study also indicates that wintering in north west Europe (e.g. Mitchell et while re-mating with previous partners can occur ai. 1995) would suggest that the potential for pre­ it is not invariable, since in two cases where pre­ viously paired individuals meeting again on the vious partners were present, the individuals pai­ wintering quarters is high. However, adult Wi­ red with other Wigeon present in the flock. This geon have an annual survival rate of c. 53% observation suggests that decisions may being (Boyd 1962), thus the chances of a partner surviv­ made as to whether it is profitable to pair again ing to the following winter are reduced. Standard with a previous partner (Coulson 1972, Black ringing techniques (using metal rings only) do not 1996). promote repeat behavioural observations of indi­ Additional observations at Eastpark Farm viduals. Individual marking techniques (espe­ were undertaken by P.Shimmings, C. & R.Hesk­ cially coloured and engraved leg bands) do allow eth, H.Mcarty, S. Cooper, 6. Einarrson, G. Siri­ repeat observations and future studies may yield wardena and J. Doherty. A. Fox, J. Black, B. Hug­ further evidence of reforming of pair bonds in hes and two anonymous referees kindly com­ other migratory duck species. mented on an earlier draft. N. Jarrett provided in­ Although pair reformation has been recorded valuable advice. in some other migratory Anas species (Dwyer et ai. 1973, Fedynich & Godfrey 1989, Kohler et ai. 1995), it appears to be rare because pair formation REFERENCES takes place in large flocks and competition be­ tween cJ cJ for mates is strong because of male­ Black J.M. 1996. Partnerships in birds: the study of biased sex ratios. Year to year stability of breed­ monogamy. Oxford University Press, Oxford. Boyd H. 1962. Population dynamics and the exploita­ ing partners may be enhanced by a habit of win­ tion of ducks and geese. In: E.D. Ie Cren & N.W. tering in a stable habitat and in relatively small Holdgate (eds) The exploitation of natural animal flocks, of which both situations occur at Eastpark populations: 85-95. Blackwell, Oxford. Farm. In this study, the Wigeon pair formations Coulson J.C. 1972. The significance of the pair bond in almost certainly took place on the wintering the Kittiwake Rissa tridactyla. Int. Onithol. Congr. 15: 423-433. grounds (i.e post wing moult and after autumn Dwyer T.J., S.R. Derrickson & D.S. Gilmer 1973. Mi­ migration) since some individuals were seen grational homing by a pair of Mallards. Auk 90: alone prior to re-mating (presumably having ar­ 687. rived prior to their mates). Ens RJ., S. Choudhury & J.M. Black 1996. Mate fidel- Mitchell: RE-MATING IN WIGEON 277 ity and divorce in monogamous birds. In: I.M. Williams M. & F. McKinney 1996. Long-term monog­ Black (ed.) Partnerships in birds: the study of amy in a river specialist - the Blue Duck. In: I.M. monogamy: 344-401. Oxford University Press, Black (ed.) Partnerships in birds: the study of Oxford. monogamy: 73-90. Oxford University Press, Ox­ Fedynich A.M. & Cl Godfrey 1987. Gadwall pair re­ ford. captured in successive winters on the southern high plains ofTexas. I. Om. 60: 168-170. Kohler P., U. Kohler, I. Pykal, E. von Krosigk & U. Firsching 1995. Sustained pair bonds during moult SAMENVATTING migration? Pair formation during break up of fam­ ily groups in Gadwall Anas strepera. lOrn 136: 167-175. Bij veel soorten eenden vindt de paarvorming plaats in McKinney F. 1986. Ecological factors influencing the het overwinteringsgebied, nadat de mannetjes het social systems of migratory dabbling ducks. In: eclipskleed hebben verruild voor het kleurige broed­ D.L Rubenstein & R.w. Wrangham (eds) Ecologi­ kleed. In het algemeen volgen de mannetjes hun cal aspects of social evolution: 73-82. Princeton vrouwtje naar haar geboortegrond, om haar te verlaten University Press, Princeton. zodra het legsel voltallig is, of wanneer de kuikens zijn Mitchell C, M. Owen & B. Etheridge 1995. Within uitgekomen. Er zijn vrijwel geen gegevens voor eenden winter movements, winter site fidelity and age ra­ ofdeze dieren elk jaar een nieuwe partner kiezen, ofdat tios of Wigeon in Britain and Ireland. report Wild­ ze elkaar weer opzoeken in het overwinteringsgebied. life & Wetland Trust, Slimbridge. De auteur onderzocht dit aan individueel gemerkte Owen M. & C Mitchell 1988. Movements and migra­ tion ofWigeon Anas penelope wintering in Britain Smienten Anas penelope, die overwinterden in Z. and Ireland. Bird Study 35: 47-59. Schotland. Van vijf paar kwamen beide partners het Rohwer CR. & M.G. Anderson 1988. Female-biased volgende jaar terug. In drie gevallen hervormde de philopatry, monogamy, and the timing of pair for­ oude paarband zich; in twee gevallen was er sprake van mation in migratory waterfowl.